This invention relates to a simple instrument for measuring the transmittance of a dye-impregnated film in such a simple, film-type integrated global solar radiation-measuring system that utilizing the fact that when the dye-impregnated film is exposed to solar radiation the dye-impregnated film is faded corresponding to the amount of the integrated solar radiation energy, the amount of the exposed integrated solar radiation energy is inferred from the degree of the color fading determined by measuring the transmittance of the film.
It is quite well-known that the amount of energy poured from the sun to the earth depends upon artificial phenomena such as an increase in the amount of carbon dioxide gas generated artificially, the destroying of the ozonesphere, the accumulation of burning products of fossil resources, and the like; and natural phenomena such as the accumulation of volcanic ash mist due to a volcanic eruption and the like, so that the natural environment surrounding human beings is changing gradually. Said change can be seized on the whole; however, the local information thereof is very little. The amount of solar radiation energy at each point in the living environment is greatly varied depending upon the configuration of the ground and the circumstances surrounding the points such as in water, in the shade of artificial structures, and the like; more specifically speaking, in the surface material of each leaf of a luxuriating plant; and the like, and it seems necessary to grasp, with an exactness to some extent, the amount of solar radiation energy in these local places and study its causual relation with various phenomena of living things, atmospheric phenomena and the like. For this purpose, a film for simply measuring the amount of solar radiation energy has already been developed which film utilizes the correlation between the degree of fading of a dye-impregnated film and the amount of the integrated solar radiation energy in the position in which the film is placed [see Yoshimura, Komiyama and Ishikawa, Solar Energy, Vol. 115, No. 5, p. 47 (1987)], and when said film is applied, it is possible to gather simultaneously data obtained in many places wherever the film may be placed. However, at present, the small pieces of the film used in the above measurements must be subjected together to measurement of absorbance by a spectrophotometer, and hence, the real situation is that the valuable benefit of simultaneous measurement at many points cannot be sufficiently utilized.
The object of this invention is to provide a simple measurement instrument aiming at simply and quickly measuring, at the measurement locales, the transmittances of simultaneous many-place-exposure samples of a dye-impregnated film having an effective exposure area of 3 cm2 or less for measuring the amount of solar radiation energy. Accordingly, the measurement instrument should have a small size and a light weight.
Moreover, as is clear from the above-mentioned object, it is necessary that the measurement precision of the instrument be such that not the mere transmittance of light but the absorbance reduced from the transmittance measured corresponds exactly to the result of measurement by a general spectrophotometer and this invention intends to obtain such a measurement instrument. If the object is to merely measure a transmittance, the measurement instrument may be relatively simple; however, in order to achieve the object of obtaining measurement values equivalent to those of a spectrophotometer by which the absorbance is determined from the transmittance measured using a sharp monochromatic light having a narrow half-value width and quantitatively determining the absorbance from them, the necessary measures must be adopted, and the main points thereof are as follows:
(1) A blue light having a wavelength of 400 to 500 nm is suitable as the monochromatic light in view of the characteristics of the absorption spectrum of the objective dye.
(2) The use of a band-pass filter is more suitable than the use of a spectral manner for taking out the monochromatic light at a low cost; however, it is difficult to obtain a band-pass filter giving a light having a narrow wavelength width and being small in reduction of quantity of light, so that it is more preferable to use a light-emitting diode (LED) which emits a monochromatic light.
(3) Though the light emitted by the light-emitting diode is a monochromatic light, its spectrum is wide, and hence, the light-emitting diode is necessarily used together with the band-pass filter. How is this problem solved, that is, how is the band-pass filter prepared for obtaining a monochromatic light having a narrower halfvalue width than the half-value width of the absorption spectrum of the objective dye for developing the necessary precision?
(4) How is a light-emitting diode which emits a blue light at a high energy obtained?